The present invention relates to refractory gas permeable structural units for blowing a gas into a metal treatment vessel and through its casing.
The oxygen blowing method used in pig iron refining which is known under the names of "LD"--, "LDAC"--, "OLP"--, "BOF"-- methods are recently improved, as far as the metallurgy is concerned in that secondary gases are blown under controlled conditions through the container bottom, like nitrogen or argon. Also in other metal treatment containers like ladles for after treatment of steel or electric arc furnaces, the blowing of gas into the metal bath through the bottom of the container or the casing of the container wall is taken into consideration.
In the patent application LU No. 81,208 applicants disclose a device which can be inserted into the bottom of a metal treatment container for blowing a treatment gas into a metal bath, which has a considerably improved stability with respect to the hitherto known gas permeable stones and which permits the blowing of the desired gas quantities. This device essentially consists of a refractory gas permeable structural unit, whereby in an axial direction of the fire proof material, a plurality of flat corrugated pipe like or wire like metallic separating members of a low wall thickness are embedded. In accordance with one embodiment, this structural unit consists of steel sheet metal and segments or strips of fire proof material in alternating arrangement.
In further LU patent applications, applicants have disclosed embodiments and variants of such gas permeable stones. In all of these embodiments the scavenger stone or the segments forming the stone, respectively, are encompassed by a metal housing which sealingly abuts against the longitudinal faces of the stone and, if necessary, with interposition of an intermediate layer of mortar. Thereby, it is achieved that the gas escapes only on the fire side of the stone, and furthermore, the undesirable and uncontrollable gas passage along the metal housing is eliminated.
These scavenger stones or the segments forming the stone are made by extrusion of fire proof material, as a rule, to which a stone fire may be connected. In accordance with this manufacturing technique, the scavenger stones and therefore the encompassing metal housings have a rectangular or square cross-section.
Because of this cross-sectional shape, a swelling of the metal housing may occur at higher gas pressures, whereby the metal housing is lifted off this scavenger stone so as to create an undesirable gap between the stone and the metal housing. The metal melt (pig iron or steel) may penetrate into this gap and the danger exists that the melt may penetrate to the cold side of the stone.
Moreover, the danger exists that the metal housing which consists of steel sheet metal is subjected to structural changes by absorbing carbon or nitrogen from the surrounding carbon containing masonry of the furnace or from the atmosphere, respectively, which impairs its stability.